[TowerTalk] Conclusion, G5RV vs. Dipole

[alsopb]

Look in the 17th addition of the antenna handbook.  The section on
antenna currents on transmission lines.

It shows that unless the feedline is at right angles to the radiators
and remains equidistant from the two halves, equal same direction
currents are induced in the feedline.  In other words, the feedline
radiates.  This happens regardless of what feedline one uses.  Coax
guys can use ferrites to quash this.  Ladder line guys can't.  A good
portion of this radiation will be vertically polarized.

I believe due to the installation difficulties of ladder line, that
obtaining near to the perfect conditions is quite difficult.  I
suspect that indeed, most of the installations do have
feedline radiation.  The questions are: How much and is it important? 
Is the criteria RF in the shack or rf burns or just what.  I wish
somebody would model this stuff once and for all to obtain
quantitative answers.

73 de Brian/K3KO





n4kg@juno.com wrote:
> 
> Unless I am mistaken, there is a HUGE misunderstanding
> of how the G5RV antenna works.
> 
> The ONLY way it could act as a Top Loaded Vertical is for
> the currents in each side of the balanced transmission line
> to be EQUAL and flowing in the SAME direction.  If that were
> the case, they could be tied together or replaced by a single
> wire and attached to the two sides of the horizontal wires at
> the top.  I do NOT believe that is the case.
> 
> IF the feed is indeed as a split balanced dipole of various
> electrical lengths, then the ladderline is acting as a balanced
> transmission line with EQUAL but OPPOSITE currents in
> each side and it does NOT radiate.
> 
> As a balanced dipole, it acts as:
> 
> 3/8 wave (short ) dipole on 80M
> 3/4 wave (long) dipole on 40M
> 2 Half Wave dipoles in phase on 30M (Voltage Node feed)
> 3 Half Wave Long Wire on 20M (current Node at feed)
> (almost) 2 Full wave LW's in phase on 17M  (near voltage node)
> 9/4 wave LW on 15M (neither current nor voltage node at feed)
> 5/2 wave LW on 12M (current node at feed)
> Two 2WL LW in phase on 10M (voltage node at feed)
> 
> BTW, as originally designed, the ladderline was meant as
> an impedance transformer that provided a reasonable SWR
> on SOME bands (but NOT ALL) without the need for a tuner.
> 
> de  Tom  N4KG
> 
> On Mon, 16 Oct 2000  David Jordan <wa3gin@erols.com> writes:
> > Right on Tom...
> >
> > A dipole at 1/8 wave above ground is a great NVIS antenna.  Two
> > dipoles at 1/8 wave above ground spaced .67 wavelength feed with open
> wire
> > line
> > and feed in phase from a center drop or open wire to a tuner is even
> > better.  Most of the radiation goes straight up and it's omni
> > directional!
> >
> > The G5RV is a top loaded vertical on the lowest freq w/ the twin
> > lead radiating as a vertical does...a real compromise if one is looking
> 
> > for short skip high angle radiation.
> >
> > Have Fun,
> > dave
> > WA3GIN
> >
> 
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